Temperature sensors, or thermometers, are known in the state of the art. A problem is that these sensors must, over the course of their use, be calibrated after certain intervals of time, as a function of the particular application, in which they are used. Calibration is difficult to accomplish, since the temperature sensor is normally installed in a plant, e.g. on a tank or pipe, and must, therefore, be deinstalled for the calibration. This implies, in most cases, that a process being performed must be interrupted. Thus, medium must be drained out of a container, or medium is not permitted to flow through a pipe. Furthermore, as a part of the deinstallation, existing seals are broken and must then be made effective again in conjunction with the reinstallation.